1. Field of the Invention
This invention relates to an improvement in a tapping screw.
2. Description of the Background Art
In fixing a metal plate member to a base plate such as steel, a tapping screw having the construction such as shown in FIG. 5 has been conventionally used. The tapping screw has a shank portion 21 which is progressively reduced in its diameter towards its tip and is equipped with a threaded portion 23 having a rough pitch, as shown in FIG. 5. The principal problem of the tapping screw of this kind is that the fastening force between the member to be fixed and the base plate is insufficient because a contact area between the shank portion 21 and a female screw portion formed in the metallic base plate upon screwing is small.